Structure Control And Sodium Ion Storage Performance Of Metal Chloride Intercalated Graphite

Graphite intercalation compounds（GICs）,a type of compact stacking lamellar material,are produced by intercalating atomic or molecular chemical species（guests）between the interlayer space in graphite without destroying the layered structure of the pristine graphite host.The metal chloride guest in the metal chloride-GIC interacts with the carbon layer,resulting in a series of new characteristics,such as high electrical conductivity,high magnetic permeability,superconductivity,wave absorption,catalysis,etc.,and there is a large interlayer space.Conducive to the reversible storage of metal ions,it is a kind of electrode material for electrochemical energy storage devices with great application prospects.However,in the process of charge and discharge,metal chloride guest is easily dissolved in the electrolyte,causing loss of active material,and ultimately resulting in extremely poor cycle performance.Therefore,the research aim is to improving the cycle stability of metal chloride-GIC as negative electrode materials,mainly from the two aspects of coating modification and composition control,to explore its sodium ion storage performance.From the perspective of surface modification,the problem of dissolution and escape of chloride is solved by coating the surface of FeCl₃-GIC with a polypyrrole（PPy）shell.Polypyrrole has a high degree ofπ-πconjugated polymer chain,which is a conductive polymer with good electronic conductivity;high electrochemical stability,almost no degradation during battery cycling;compact structure,capable of maintaining the GIC structure from the perspective of physical limitations Integrity;Contains a large number of pyrrole nitrogen polar groups,which can effectively anchor the easily soluble FeCl₃component from the perspective of chemical adsorption and help maintain the cycle stability of FeCl₃-GIC.Under different conditions,FeCl₃-GIC was coated with polypyrrole by in-situ polymerization to prepare core-shell structure（FeCl₃-GIC）@PPy.By comparing the microstructure between FeCl₃-GIC and different（FeCl₃-GIC）@PPy And the difference of electrochemical performance,study the influence of polypyrrole coating on the electrochemical performance of FeCl₃-GIC.Specially,the specific capacity of（FeCl₃-GIC）@PPy remains steady with a high sodium storage value of 281mA·h·g^-1after 100 cycles at the current density of 0.1 A·g^-1,while the FeCl₃-GIC anode shows a continuous capacity decay with a low value of 157mA·h·g^-1after 100 cycles.Additionally,even at a high current density of 1.0 A·g^-1,the（FeCl₃-GIC）@PPy anode delivers a remained sodium storage capacity of 181mA·h·g^-1after 500 cycles,accompanying with a fascinating capacity retention ratio of 89%.The multi-element metal chloride has the characteristics of melting eutectic,and its application in the intercalation reaction can significantly reduce the required reaction temperature of the system and save energy.This article attempts to use AlCl₃as the MoCl₅intercalation promoter to reduce the temperature of MoCl₅intercalation graphite,and prepare AlCl₃-MoCl₅-GIC with higher energy storage activity through a low energy consumption process.Studies have shown that when using a hybrid method to synthesize AlCl₃-MoCl₅-GIC with natural flake graphite as the host and AlCl₃and MoCl₅as intercalating agents,the reaction temperature,holding time,and the ratio of graphite to metal chloride affect the product structure and lithium/sodium storage.The intercalation reaction may have an intercalation reaction mechanism in which the intermediate product Al MoCl₈is generated and part of AlCl₃is replaced by MoCl₅.Compared with MoCl₅-GIC and AlCl₃-GIC,the conductivity of AlCl₃-MoCl₅-GIC is significantly improved,and it has good air stability.Similarly,AlCl₃-MoCl₅-GIC was coated with polypyrrole polymerized to explore the electrochemical lithium/sodium storage performance of（AlCl₃-MoCl₅-GIC）@PPy.When AlCl₃-MoCl₅-GIC stores lithium,the first coulombic efficiency is 63.6%,and the capacity retention rate is only 27.2%after 100 cycles.The first coulombic efficiency of（AlCl₃-MoCl₅-GIC）@PPy in lithium storage after polypyrrole coating is66.5%,and the capacity retention rate is 87.4%after 100 cycles.When AlCl₃-MoCl₅-GIC stores sodium,the capacity retention rate is only 24.7%after 100cycles.However,after coating with polypyrrole,the capacity retention rate of（AlCl₃-MoCl₅-GIC）@PPy in sodium storage increased to 97.1%after 100 cycles.